This invention relates to broadly defined adhesive latex formulations exhibiting antimicrobial properties. Such formulations comprise, as the only antimicrobial active ingredients, certain inorganic antimicrobial compounds, such as, preferably, metal-containing ion-exchange and/or zeolite compounds. The inventive latex formulations must also exhibit substantially uniform characteristics (such a similar viscosity and/or appearance throughout) in order to provide a functionally and aestheticially pleasing formulation for utilization within any number of applications. In order to provide such an inventive latex formulation, it has been found that compounding of all the base ingredients (polymer, antimicrobial agent, fillers) must be undertaken prior to the final thickening, step, which ultimately produces the desired latex. The specific method of producing such formulations is also encompassed within this invention.
All U.S. Patents listed below are herein entirely incorporated by reference.
There has been a great deal of attention in recent years given to the hazards of bacterial contamination from potential everyday exposure. Noteworthy examples of such concern include the fatal consequences of food poisoning due to certain strains of Eschericia coli being found within undercooked beef in fast food restaurants; Salmonella contamination causing sicknesses from undercooked and unwashed poultry food products; and illnesses and skin infections attributed to Staphylococcus aureus, Klebsiella pneumoniae, yeast, and other unicellular organisms. With such an increased consumer interest in this area, manufacturers have begun introducing antimicrobial agents within various household products and articles. For instance, certain brands of polypropylene cutting boards, liquid soaps, etc., all contain antimicrobial compounds. The most popular antimicrobial for such articles is triclosan. Although the incorporation of such a compound within liquid or certain polymeric media has been relatively simple, other substrates, including the surfaces of textiles and fibers, have proven less accessible. Furthermore, triclosan includes chlorine ions which, upon dissociation, may release to the substrate surface. Such ions are potentially hazardous to humans, due to skin irritation upon contact, as well as within environmental effluents, and the like. Additionally, harmful microbes have shown, on occasion, an ability to develop an immunity to the bactericidal properties of triclosan. Also, surface treatments with triclosan have proven ineffective as well since such compounds are highly water soluble and are easily removed upon exposure to sufficient amounts of moisture and high temperatures. There thus remains a long-felt need to provide a short-and long-term effective, durable, and long-lasting antimicrobial agent for surface utilization within adhesive latex formulations. Of additional importance is the need to provide such formulations which, upon exposure to high temperature processing conditions (either in the production of or incorporation of such formulations within other applications, such as carpet backing, and the like) do not require the presence of organic bactericides which may result in the release of a certain volatile organic content (VOC) upon such high temperature processing.
One proposed latex has utilized metal ions for bactericidal properties, but also requires the presence of an organic bactericide to provide the desired level of antimicrobial activity. U.S. Pat. No. 5,736,591 to Dunn teaches the addition of certain metal ions, including copper, silver and any other Group Ib metals, as salts (such as silver nitrate, silver perchlorate, and the like) to latex formulations in combination with Such organic compounds as 2-methyl-4, 5-trimethylene-4-isothiazolin-3-one, to provide a bactericidal latex. No mention is made anywhere within this patent of the availability, much less, the capability of silver-based ion-exchange or zeolite compounds as potential antimicrobial agents. Nor is there any discussion of the ability of any such silver-based compounds providing effective antimicrobial activity without the need for any added organic bactericides.
Such specific silver-containing inorganic microbiocides (e.g., ion-exchange and/or zeolite compounds) have recently been developed and utilized as antimicrobial agents on and within a plethora of different substrates and surfaces. In particular, such microbiocides have been adapted for incorporation within plastic compositions and fibers in order to provide household and consumer products which inherently exhibit antimicrobial characteristics. Although such silver-based agents provide excellent, durable, antimicrobial properties, to date no teachings exist which teach or fairly suggest the presence of such inorganic compounds within adhesive latex fomulations. This is not surprising considering the difficulties which have been noted in attempting such an introduction of these large molecular weight, bulky, compounds within polymer latex formulations to begin with. For instance, such inorganic compounds may interfere with the desired adhesives qualities of the latex if and when such large molecules are present at the surface. One would anticipate that a large surface accumulation of such bulky compounds would reduce the potential surface-to-surface interaction required for the adhesive formulation to function properly. Furthermore, it has been found that the addition of such bulky compounds within already-compounded latex formulations is extremely difficult. The resultant composition generally exhibits discrete areas of concentrated, dark-colored, antimicrobial compound. Not only does this result in an unpleasing aesthetic appearance, but such a latex, being nonuniform in dispersion as well, may exhibit uneven adhesive properties, too. Although these problems exist, there is a desire to incorporate such silver-based inorganic antimicrobial agents within adhesive latex formulations in order to provide a regenerable, highly effective, long-lasting antimicrobial latex at, on, or within various different articles. Unfortunately, to date, no such antimicrobial adhesive latex or methods of production or use thereof have been accorded the latex industry by the pertinent prior art.
It is thus an object of the invention to provide a simple manner of producing an effective adhesive latex comprising, as the sole antimicrobial agent, at least one inorganic silver-based ion-exchange compound or zeolite compound. Another object of the invention is to provide an antimicrobial adhesive latex exhibiting a substantially uniform appearance and possessing no VOC content.
Accordingly, this invention encompasses an adhesive latex fomulation comprising at least one polymer constituent, at least one thickening agent (in order to provide a latex having a viscosity of, preferably, at least 4,000 cps at 25xc2x0 C. and at 1 atmosphere), and at least one inorganic silver-based antimicrobial agent selected from the group consisting of silver-based ion-exchange compounds, silver-based zeolites, silver-based glasses, and any mixtures thereof, wherein said formulation does not include any VOC (due to the absence of any organic bactericide compounds, primarily). This invention also encompasses a method of producing such an antimicrobial adhesive latex formulation comprising the steps of (a) providing a polymer constituent, compounding said polymer constituent with an inorganic silver-based antimicrobial agent (as noted above) and a thickener, simultaneously, until the resultant composition exhibits a viscosity of, preferably, at least 4,000 cps at 25xc2x0 C. and at 1 atmosphere.
The term adhesive latex is intended to encompass any thickened formulation of already-made polymer constituents which possesses a viscosity of at least viscosity of, preferably, at least 125,000 cps at 25xc2x0 C. and at 1 atmosphere and which also exhibits an affinity for different surfaces which results in the ability to create a stationary interaction between the latex and the target surface without the needed presence of any other adhesive initiators, additives, compounds, or other compositions. Such latices are well known throughout the pertinent art (such as within U.S. Pat. No. 5,736,591) and may be utilized within any variety of applications which require extremely thick adhesives, including, without limitation, carpet backings, sealant compositions (for ceramic tiles, for example), and the like. The term polymer constituent is intended to encompass any polymeric material capable of being in latex form. Such constituents thus include, without limitation, olefins, acrylics, urethanes, vinylidene chlorides, vinyl acetates, vinyl pyridines, aromatics, silicones, and any copolymers thereof. Most preferably, the latex is a styrene butadiene rubber (SBR) latex, a polyurethane latex, a vinylidene chloride latex, a polyvinylidene chloride latex, a carboxylated SBR latex, and the like. Such polymer constituents within this invention include, without limitation, and preferably, HPL 8455NA (a vinylidene chloride) from Dow, and Reichold R101 (SBR rubber). The amount of polymer constituent present within the inventive latex ranges from about 10 to about 65% by weight of the total composition. Preferably, this amount is from about 20 to about 60%; more preferably from about 25 to about 50%; most preferably from about 30 to about 50%. It is common for such pre-prepared polymer constituents to include biocide agents solely for the purpose of preserving such compounds upon long-term storage.
Such latices arc preferably of high solids content to provide high adhesive properties. As such, the latex should be, as noted above, of rather high viscosity in order to stabilize the solid compounds in composition. Such a viscosity, as measured at 25xc2x0 C. and at 1 atmosphere pressure, is at least 4,000 cps; preferably between about 4,500 and 25,000 cps; more preferably from about 5,000 cps to about 15,000 cps; and most preferably from about 5,000 cps to about 12,000 cps. The necessary thickener added to the polymer constituent is thus of prime importance. A thickener such as polyacrylate salt (sodium for example) is highly preferred, although any standard latex thickening agents may be utilized for this purpose. The amount of thickener is highly dependent on the desired target viscosity. Generally, then, the amount should be from about 0.005 to about 5% by weight of the total latex formulation; preferably from about 0.01 to about 3%; more preferably from about 0.015 to about 1%; and most preferably from about 0.02 to about 0.5%.
The term inorganic silver-based antimicrobial material is intended to encompass any such silver-conatining solid compound which is primarily inorganic in nature (some organic component is permitted, although the primary antimicrobial portion must be inorganic), is a solid at standard temperature and pressure, and which exhibits antimicrobial activity. Preferably, such material is a silver-based ion-exchange compound, a silver-based zeolite, or a silver-based glass, and any combinations thereof The preferred silver-based ion exchange material is an antimicrobial silver zirconium phosphate available from Milliken and Company, under the tradename ALPHASAN(copyright). Other potentially preferred silver-containing solid inorganic antimicrobials in this invention is a silver-substituted zeolite available from Sinanen under the tradename ZEOMIC(copyright) AJ, or a silver-substituted glass available from Ishizuka Glass under the tradename IONPURE(copyright), may be utilized either in addition to or as a substitute for the preferred species. Other possible compounds, again without limitation, are silver-based materials such as AMP(copyright) T558 and MICROFREE(copyright), both available from DuPont, as well as JMAC(copyright), available from Johnson Matheny. Generally, such a metal compound is added in an amount of from about 0.00001 to 10% by total weight of the particular latex composition; preferably from about 0.001 to about 5%; more preferably from about 0.01 to about 1%; and most preferably from about 0.1 to about 1.0%.
Other possible components within the inventive latex composition include water, (as a diluent), fillers, such as calcium carbonate (to provide strength and hardness to the latex, as well as to fill any xe2x80x9cempty spacesxe2x80x9d for a uniform strength dispersion), flame retardants, such as antimony oxide, available from Great Lakes Chemical, emulsifiers and/or surfactants (to provide more effective interaction with target surfaces and/or to provide foaming for easier application to target surfaces). Of these components, the fillers are generally added in large amounts within such latex formulations for the strength and hardness purposes.
As noted above, such an inventive comprises no organic bactericide compounds and thus does not include any appreciable VOC content originating from the antimicrobial component. This is of vital importance to ensure that utilization of such a latex does not result in the release of environmentally and/or physically hazardous organics, particularly upon exposure to high temperatures (e.g., above about 100xc2x0 C.).
The inventive adhesive latex is preferably compounded with all of the required components simultaneously added together in order to provide the most uniform product, from both appearance and physical performance perspectives. Thus, simultaneous compounding of the polymer constituent, thickener, and silver-based inorganic antimicrobial agent are required (as well as the other potential additives) for this purpose. Adding such solid antimicrobial agents after compounding is extremely difficult without the production of highly undesirable discolorations (e.g., darkening, particularly if high temperatures are utilized for further processing).
The particular silver-based inorganic antimicrobial agent should exhibit an acceptable log kill rate after 24 hours in accordance with the AATCC Test Method 100-1983. Such an acceptable level log kill rate is tested for Staphylococcus aureus or Klebsiella pneumoniae of at least 0.1 increase over baseline. Alternatively, an acceptable level will exist if the log kill rate is greater than the log kill rate for non-treated (i.e., no solid inorganic antimicrobial added) latices (such as about 0.5 log kill rate increase over control, antimicrobial-free latices). Preferably these log kill rate baseline increases are at least 0.3 and 0.3, respectively for S. aureus and K. pneumoniae; more preferably these log kill rates are 0.5 and 0.5, respectively; and most preferably these are 1.0 and 1.0, respectively. Of course, the high end of such log kill rates are much higher than the baseline, on the magnitude of 5.0 (99.999% kill rate). Any rate in between is thus, of course, acceptable as well. However, log kill rates which are negative in number are also acceptable for this invention as long as such measurements are better than that recorded for correlated non-treated latices. In such an instance, the antimicrobial material present within the latex at least exhibits a hindrance to microbe growth.
The preferred embodiments of these alternatives fabric treatments are discussed in greater detail below.